Computer systems are generally designed under the premise that accesses to memory are limiting factors in the efficiency of the computer system. Common computer systems are designed to take advantage of fast-cache memory while still allowing for large memory sizes. To provide this advantage computer systems are designed with a memory hierarchy. Generally, the memory hierarchy is implemented using a progression of several levels of memory having increasing storage capacity and decreasing access speeds. Typical components include cache located within the processor die, sometimes referred to as internal cache, externally located cache, random-access memory (RAM) and mass memory storage devices. Other memories include memories used by various peripheral devices and processors, such as graphics adapters, communications adapters and other input/output components. From the perspective of the processor executing a software program, these memories are often hidden in the sense that common data is temporarily cached in smaller and faster memory circuits. This common data is mapped to larger and slower memory circuits, which are accessed when the faster memory does not contain the desired data. The common data, if changed in the cached memory, can eventually be written to the larger and slower memory circuits. This allows for the slow memory access time to be hidden so long as the faster memory contains the appropriately mapped data.
Computer systems generally contain some type of mass-storage memory that is able to retain data when the computer system is powered down. This type of memory is referred to as nonvolatile memory because it is able to maintain data integrity when the computer system is not powered. Nonvolatile memory, however, can be slower by orders of magnitude relative to various volatile memories. Yet, nonvolatile memory can also be less expensive (per unit of memory capacity) and/or less power hungry. A common type of nonvolatile mass-storage memory is a hard disc drive (HDD) that uses a rotating magnetic media. HDDs are used for home-computers, servers, and various other devices. Under normal operation, a computer system transfers sensitive data from temporary memory to a HDD before the computer system is powered down. This allows for the sensitive data to be saved in memory that persists after the power is removed from the computer system. When the computer system is subsequently powered up, this data can be accessed and used by the computer system.
HDDs with rotating magnetic media have been in use for many years and have undergone various improvements including efficiency, reliability and memory capacity. Various applications, however, are beginning to use other types of nonvolatile memory with more frequency. Solid State Devices/Drives (SSDs) are one such alternative nonvolatile memory. SSDs are attractive for many applications because, unlike HDDs, they have no need for moving parts with HDDs. Thus, they are not subject to mechanical wear inherent in HDDs. Another advantage of SSDs over traditional HDDs is that physical movement, e.g., shock or vibration, of the HDD can interrupt accesses to the rotating media. Thus, HDDs often include various mechanisms to compensate for mechanical shocks. Speed, cost and power requirements also factor into the selection of SSDs or HDDs.
While SSDs have their advantages over HDDs, there are a number of reasons why they have not yet completely replaced HDDs with rotating magnetic media. Aspects of the present invention, although not limited thereto, can be appreciated in the context of such mass-memory storage devices.